Field of the Invention
The present invention relates generally to methylome analysis, and more specifically to a method for detecting cancer through generalized loss of stability of epigenetic domains of the genome.
Background Information
Epigenetics is the study of non-sequence information of chromosome DNA during cell division and differentiation. The molecular basis of epigenetics is complex and involves modifications of the activation or inactivation of certain genes. Additionally, the chromatin proteins associated with DNA may be activated or silenced. Epigenetic changes are preserved when cells divide. Most epigenetic changes only occur within the course of one individual organism's lifetime, but some epigenetic changes are inherited from one generation to the next.
One example of an epigenetic mechanism is DNA methylation (DNAm), a covalent modification of the nucleotide cytosine. In particular, it involves the addition of methyl groups to cytosine nucleotides in the DNA, to convert cytosine to 5-methylcytosine. DNA methylation plays an important role in determining whether some genes are expressed or not. Abnormal DNA methylation is one of the mechanisms known to underlie the changes observed with aging and development of many cancers.
Cancers have historically been linked to genetic changes such as DNA sequence mutations. Evidence now supports that a relatively large number of cancers originate, not from mutations, but from epigenetic changes such as inappropriate DNA methylation. In some cases, hypermethylation of DNA results the an inhibition of expression of critical genes, such as tumor suppressor genes or DNA repair genes, allowing cancers to develop. In other cases, hypomethylation of genes modulates expression, which contributes to the development of cancer.
Cancer is generally viewed as over 200 separate organ-specific diseases of abnormal cell growth, largely controlled by a series of mutations, but also involving epigenetic, i.e. non-sequence based, changes that might involve the same sets of genes'. DNA methylation at CpG dinucleotides in particular has been studied extensively in cancer, with hypomethylation reported at some genes, hypermethylation at others, and a global loss of DNA methylation ascribed to repetitive DNA elements that are normally methylated.
Since the discovery of altered DNA methylation in human cancer, the focus of cancer epigenetics has been on candidate regions of the genome, either high-density CpG islands, gene promoters, or dispersed repetitive elements2,3, and there has not been a comprehensive genome-scale understanding of the relationship between DNA methylation loss and gain in cancer and in normal differentiation.